Optogenetics refers to a cutting-edge set of molecular methods that allows for light-based control of targeted neurons in intact brains. These methods have immense potential as a basic research tool to determine the role of specific neuronal populations in healthy and abnormal brain function. In addition, further development of these methods may lead to new types of treatments for neurological and psychiatric disorders, as well as a new class of prostheses for those with sensory impairments. This project is aimed at further developing these methods so that they can achieve their basic research and clinical potential. This proposal introduces key improvements in the molecular methods as well as fundamental improvements in their application to the study of higher-order perceptual and cognitive functions. Critically, the approach of this proposal is minimally invasive and hence, unlike previous methods, causes little to no tissue damage. In addition, the improvements introduced by this proposal allow for more precise targeting of neurons and more potent control of the responses of those neurons. This proposal uses these methods to systematically determine their efficacy at both the neuronal and the behavioral levels. A key innovation of this approach is the development of an optogenetic window. This window will permit long-term health of the cortex, functional mapping prior to delivery of molecular agents, precise targeting of molecular agents to specific functional sites, and assessment with established optical imaging, electrophysiological, and behavioral methods. This proposal will allow patterns of neuronal modulation (both inhibitory and excitatory) to be related to specific perceptual and behavioral effects. The successful completion of this project will have enormous benefits for basic research into higher-order perceptual and cognitive functions, and will provide a solid foundation for the development of new treatments for the sensory impaired as well as those with psychiatric or neurological disorders.